This invention relates to a gas laser tube and more particularly to an improvement for a laser output mirror portion thereof.
In a gas laser tube, a diameter of an output mirror is generally several ten times as large as the diameter of a laser beam thereon. This is for eliminating the problem of reduced gain in laser oscillation as well as for setting a larger tolerance for assembly errors.
The light outputted from the output mirror is not limited to a coherent light, or laser beam but includes incoherent light generated by gas discharge. Since the incoherent light has no directivity, it is desirable to minimize the incoherent light. The output of such an incoherent light may be reduced by decreasing the diameter of the output mirror, but it could entail such problems as the reduced gain in laser oscillation and difficulties in assembly, and thus such measurement is not practical.
There has not been seen in commercial market to use a mask attached with the output mirror instead of reducing its diameter. This is because optical axes of output mirrors of a plurality of produced gas laser tubes are differently aligned to each other due to assembly errors, and thus it becomes very expensive to manufacture a mask properly aligned to each output mirror. For this reason, there has heretofore been taken no particular countermeasures against such undesirable incoherent light.